1. Field of the Invention
The present invention relates to a color imaging element and an imaging device, and specifically relates to a color imaging element that can reduce occurrence of color moire and achieve high resolution, and a color imaging device including the color imaging element.
2. Description of the Related Art
In a single-plate color imaging element, since a monochromatic color filter is set on each pixel, each pixel has only monochrome color information. Therefore, since an output image of the single-plate color imaging element is a RAW image (mosaic image), a multi-channel image is acquired by processing (demosaicing process) that interpolates a missing color pixel with a surrounding pixel. In this case, there is a problem in reproduction characteristic of an image signal of high frequency, and, since aliasing is likely to occur in a taken image in a color imaging element as compared with a black-and-white imaging element, there is an important problem that a reproduction band is widened for high resolution while suppressing occurrence of color moire (false color).
In a primary color Bayer array that is a color array of a color filter that is used in a single-plate color imaging element most widely, since green (G) pixels are disposed in a checkered pattern and red (R) and blue (B) are disposed in a line-sequential manner, there is a problem in reproduction precision when generating a high frequency signal in which G signals are in an oblique direction and R and B signals are in a horizontal direction and a vertical direction.
In a case where a black-and-white stripe pattern (high-frequency image) as illustrated in (A) of FIG. 12 enters a color imaging element having a color filter of a Bayer array illustrated in (B) of FIG. 12, when this is distributed to a Bayer color array and comparison is performed every color, as illustrated in (C) to (E) of FIG. 12, R becomes a mosaic color image of light and flat, B becomes a mosaic color image of dark and flat, and G becomes a mosaic color image of light and shade. While it is originally a black-and-white image, concentration difference (level difference) is not caused among RGB but it enters a state where it is colored depending on the color array and input frequency.
Similarly, in a case where an oblique black-and-white high-frequency image as illustrated in (A) of FIG. 13 enters an imaging element having a color filter of a Bayer array illustrated in (B) of FIG. 13, when this is distributed according to the Bayer color array and comparison is performed in each color, as illustrated in (C) to (E) of FIG. 13, R and B become a color image of light and flat and G becomes a color image of dark and flat. If a value of the black is assumed to be 0 and a value of the white is assumed to be 255, only G becomes 255 and therefore oblique black-and-white high-frequency image becomes green. Thus, in the Bayer array, it is not possible to correctly reproduce an oblique high-frequency image.
In general, it is avoided by disposing an optical low-pass filter including a birefringent material such as crystal in front of a color imaging element and optically decreasing high frequency in an imaging device using a single-plate color imaging element. However, it is possible to mitigate coloring by aliasing of high-frequency signals in this method, but there is a problem that resolution degrades due to its negative effect.
To solve such a problem, there is suggested a color imaging element where an color filter array of the color imaging element is assumed to be a three-color random array satisfying array restriction conditions in which an arbitrary target pixel is adjacent to three colors including a color of a target pixel on any of four sides of the target pixel (Japanese Patent Application Laid-Open No. 2000-308080: PTL 1).
Moreover, there is suggested an image sensor of a color filter array (color imaging element) where the image sensor includes a plurality of filters with different spectral sensitivities, and a first filter and a second filter among them are alternately disposed in a first period in one diagonal direction of a pixel grid of the image sensor and are alternately disposed in a second period in other diagonal direction (Japanese Patent Application Laid-Open No. 2005-136766: PTL 2).
In addition, there is suggested a color array where, in a color solid-state imaging element of three primary colors of RGB (color imaging element), a set of three pixels in which R, G and B are horizontally disposed are disposed in a zigzag manner in a vertical direction to make appearance probabilities of RGB respectively equal and to cause an arbitrary line (horizontal, vertical and oblique lines) on an imaging plane to pass through all colors (Japanese Patent Application Laid-Open No. 11-285012: PTL 3).
Furthermore, there is suggested a color imaging element where R and B among three primary colors of RGB are disposed every three pixels in horizontal and vertical directions and G is disposed between R and B (Japanese Patent Application Laid-Open No. 8-023543: PTL 4).